To make an impression of a dental structure, a modeling procedure is typically employed. Traditionally, impressions have been made with wax, plaster reversible and irreversible hydrocollids and elastomeric or rubber-like materials. The impression materials are placed in the mouth around the dental structure to be modeled and allowed to cure. Currently, the preferred procedure for preparing an impression of a dental structure is to employ a self-setting elastomeric polymer. This polymer is introduced into the mouth of the dental patient and applied to the surface of the formation to be modeled. The polymer is allowed to harden or cure, an impression is formed, then removed and sent to a dental lab where it is used as a mold for the prosthetic device. The impression is the negative image for the preparation of the positive model.
This technique has several drawbacks: Typically, the materials work best in a dry field, since the mouth is wet, a dry field is difficult to obtain Foreign material, temperature, humidity, poor fill, patient movement and practitioner error all contribute to inadequate impressions. Furthermore, once a conventional impression is made, it can only be used once, and occasionally twice, before details are compromised, damaged or distorted, thus limiting multiple uses.
Another consideration in the conventional casting process is the time lost in physically sending the impression to the laboratory. Shipment necessarily increases the inconvenience for the patient who, in most instances, will endure the discomfort of a temporary prosthesis and perhaps even experience a change in oral features if the transit and laboratory times are particularly protracted.